Many exogenous factors can negatively impact a person's health. For instance, communicable diseases such as influenza and the common cold can rapidly spread throughout groups of people who gather in a location, such as coworkers in an office, classmates in a classroom, diners in a restaurant, or passengers on an airplane. While measures can be taken, such as frequent hand washing and getting plenty of sleep, to improve one's odds of not getting sick, even the most careful measures will occasionally fail, and communicable diseases inexorably spread, particularly as the seasons turn colder and people spend more time indoors. The resultant cost to individuals and society as a whole in lost productivity and suffering is immeasurable.